The present invention relates to a magnetic brush developing apparatus, and more particularly to a magnetic brush developing apparatus provided with means for separating from a magnetic developer in the apparatus foreign materials which cause various troubles during operation of the apparatus.
The magnetic developers heretofore known for use in magnetic brush developing apparatus include single-component developers consisting only of a magnetic toner, two-component developers comprising an insulating toner and a magnetic carrier admixed therewith, and composite developers comprising a mixture of several kinds of toners including a magnetic toner. Such a developer is used for developing latent electrostatic images on an image bearing surface into visible images while being circulated within the magnetic brush developing apparatus. As the developer is repeatedly circulated for a long period of time, more and more foreign materials become mingled with and accumulate in the developer.
Typical of such foreign materials are agglomerates of developer gradually formed during the repeated circulation of the developer from toner particles which are subjected to physical forces or heat during the circulation and which are thereby joined with one another, the agglomerates usually having about 10 times the diameter of the toner particles, and fibers of copy paper which become incorporated in the developer in a progressively increasing amount and which generally have a length nearly 10 times the diameter of the toner particles. Fibers of copy paper become incorporated in the developer especially markedly in a magnetic brush developing apparatus for transfer-type electrophotographic copiers in which the developer remaining on the surface of the photoconductive member is recovered for reuse after the transfer of the toner image.
In a transfer-type electrophotographic copier or the like, such foreign materials, if present in large quantities in the developer, cause various troubles, such as impaired transportability of the developer itself, uneven density in developed images and blank portions in transferred image areas. In a magnetic brush developing apparatus, therefore, it is very important to prevent the foreign materials from accumulating in the developer.